Accept a config filename as an optional parameter to Ghost start-up.

Closes #1110.
- Promotes config-loader from a validator, to the central place where configuration state is held
- Allow config-loader two means to be told of config file to be used:
  - A preferred first argument passed into Ghost
  - A secondary GHOST_CONFIG environmental variable
- Failing to see either of the above passed in, config-loader will continue to use "config.js"
- Config-loader validates the target configuration (unchanged) & then copies that object into it's own exports
- Components needing to read configuration now require config-loader to retrieve the configuration state
- Config file continues to be loaded via require(): this is assumed to be a static json file

core/server/config/loader.js

@@ -7,7 +7,7 @@ var fs      = require('fs'),
 
     appRoot = paths().appRoot,
     configexample = paths().configExample,
-    config = paths().config;
+    configFile =  process.env.GHOST_CONFIG || paths().config;
 
 function writeConfigFile() {
     var written = when.defer();
@@ -30,7 +30,7 @@ function writeConfigFile() {
         });
         read.on('end', written.resolve);
 
-        write = fs.createWriteStream(config);
+        write = fs.createWriteStream(configFile);
         write.on('error', function (err) {
             /*jslint unparam:true*/
             return errors.logError(new Error('Could not open config.js for write.'), appRoot, 'Please check your deployment for config.js or config.example.js.');
@@ -50,12 +50,11 @@ function validateConfigEnvironment() {
         parsedUrl;
 
     try {
-        config = require('../../../config')[envVal];
+        config = require(configFile)[envVal];
     } catch (ignore) {
 
     }
 
-
     // Check if we don't even have a config
     if (!config) {
         errors.logError(new Error('Cannot find the configuration for the current NODE_ENV'), "NODE_ENV=" + envVal, 'Ensure your config.js has a section for the current NODE_ENV value');
@@ -92,7 +91,7 @@ function loadConfig() {
         pendingConfig;
     /* Check for config file and copy from config.example.js
         if one doesn't exist. After that, start the server. */
-    fs.exists(config, function checkConfig(configExists) {
+    fs.exists(configFile, function checkConfig(configExists) {
         if (!configExists) {
             pendingConfig = writeConfigFile();
         }